MOUNT GEEYLOCK. 179 



numerous minor folds which do not show the continuity seen in P and Q. It 

 will be observed that the direction of these two main synclines represented 

 by P and Q is north-northeast to south-southwest, thus nearly parallel with 

 the direction of the valley lying between the Clarksburg- granitoid mass 

 and Hoosac mountain, and that at the .south end they converge, and perhaps 

 unite in the narrow schist ridge between Berkshire and Lanesboro vil- 

 lages. Traversing the folds of this canoe-like complex synclinorium is a 

 cleavage-foliation, sometimes microscopically minute, dipping almost uni- 

 formly east. This cleavage-foliation is distinct from the "slaty-cleavage" 

 early described by Sedgwick, Sharpe, and Sorby and reproduced experi- 

 mentally by Tyndall and Jannetaz, but consists sometimes of a minute, 

 abrupt, joint-like fracturing of the stratification laminae, but more gener- 

 ally of a faulting of these lamina? as the result of their extreme plication — a 

 mode of cleavage "Ausweichungsclivage" (slip cleavage) so well described 

 by Heim and recently reproduced in part by Cadell 1 by a slight modification 

 of the experiments made by Prof. Alphonse Favre, of Geneva, in 1878. 2 This 

 fault-cleavage, when carried to its extreme, results in a form of cleavage 

 very nearly approaching, although not identical with, slaty-cleavage. To 

 the unaided eve all traces of stratification-foliation are lost, and even under 

 the microscope they are so nearly lost as to be of no avail in determining 

 the dip. 



LITHOLOGIC STRATIGRAPHY. 



As may be inferred from the descriptions of the sections, there arc five 

 more or less clearly defined horizons in 'the Greylock mass. These are 

 described below, beginning with the lowest. 



The Vermont formation. — The feld spathic quartzite of the northwest end 

 of Deer hill, which corresponds to the quartzite of Clarksburg and Hoosac 

 mountains and of Stone hill, will be noticed more particularly in Appendix 

 A, on Stone hill. This is Emmons's "Granular Quartz," and has recently 

 been shown to be of Lower Cambrian age. 



The Stockbridge limestone. — The crystalline limestone of the Hoosac and 

 Green river valleys, which has long been known to constitute the base of 

 Mount Greylock, is the Stockbridge limestone of Emmons, and extends 



1 Op. cit. (see j>. 137), third series of experiments, 

 j^lpkonse Favre: The formation of mountains, Nature, vol, I'.'. 1878, p. 103. 



